This invention relates to integrated circuits, particularly to static random access memory (SRAM) devices, in either embedded form or stand alone (i.e. discrete) form.
As integrated circuits (ICs) become physically larger and more complex, the amount of power used by an IC increases. Power consumption in an IC may increase for several reasons. For example, the frequency at which an IC switches consumes power by charging and discharging capacitance on the IC. Increasing the switching frequency increases the power consumed on an IC. Power may also be consumed due to DC (direct current) conditions such as leakage in transistors and voltage dropped across resistors.
Power reduction may be achieved by reducing power supply voltages provided to the IC. For example, the voltage applied to an SRAM (Static Random Access Memory) may be reduced when the SRAM is not being accessed. Power may also be reduced by reducing the switching frequency. For example, in some circumstances a clock that is used to switch a particular circuit may be shut off or its frequency may be reduced.
Power reduction is particularly important in the design of DSP (Digital Signal Processor) ICs with large memory arrays. The power used by large memory arrays may be reduced by putting them into a “sleep” mode or a “retain” mode where the voltage applied to the array is reduced. However, it is important to manage when and how long large memory arrays are in the sleep mode. When large memory arrays are put into the sleep mode and taken out of the sleep mode too often, switching power is used that can negate the power saved by putting the large memory arrays in the sleep mode.
Power reduction is important in order to reduce the heating of an integrated circuit. Reducing the heating of an integrated circuit can lower the cost of packaging for an integrated circuit.